The present invention relates to a laser machining head, more specifically to a laser machining head suitable for welding steel products and the like, and for thermal machining such as cutting, gouging, spraying, and the like.
Laser machining makes possible, a machining of a very high precision, since input energy density is higher than 10.sup.2 to 10.sup.4 kJ/s-cm.sup.2 and laser light can be focused to the machined part using an appropriate optical system. Therefore, a laser machining head having such functions has heretofore been used in thermal machining such as cutting, grouging, spraying, and the like.
On the other hand, in plasma machining, when an electrical voltage is applied between electrodes to generate an arc and a working gas is fed in the periphery thereof, the working gas is ionized to produce a plasma as an electroconductive gas mixture of ions and electrons, The input energy density is about (0.5 to 1).times.10.sup.2 kJ/s-cm.sup.2. A plasma machining head, generating such a plasma, has been used for welding, cutting, and other thermal machining.
Plasma welding is a welding performed by using heat of plasma arc, and includes a plasma arc welding utilizing a transfer arc and a plasma jet welding, in which high temperature, high-speed gas flow is generated by a non-transfer arc, and welding is performed by the heat.
In general, in laser machining, a laser machining head is used alone, and similarly in plasma machining, a plasma machining head is used alone, to perform thermal machining such as welding, cutting, or gouging.
However, the above-described prior art laser machining head or plasma machining head had the following problems. Specifically, when laser welding is performed by the prior art laser machining head, welding groove targeting tolerance, that is, tolerable range when the laser beam comes out from the welding groove target line (allowance including tolerable error) is narrow. Further, when welding is performed by using an inert gas for the purpose of oxidation prevention of the welded part or preventing adherence of impurities, a porosity is generated in the welded part.
Further, when cutting is performed by using the above prior art laser machining head, plate thickness, which can be cut by a laser, is about 12 mm for a carbon dioxide (CO.sub.2) gas laser, and about 4 to 6 mm for a YAG (yttrium-aluminum garnet) laser, and cutting of steel products of greater plate thicknesses has been difficult. Therefore, it has been inferior to the plasma cutting.
On the other hand, when welding is performed by using the prior art plasma machining head, the plasma arc tends to fluctuate with insufficient stability. Therefore, tolerance of machining condition is narrow, and high precision welding is thus impossible. Furthermore, plate thickness, which is possible for 1-pass welding has been only about 3 to 4 mm.
A primary object of the present invention, is to solve the above prior art problems, and to provide a laser machining head, in which focused laser light and plasma arc are coaxially disposed to reinforce laser light with plasma arc to form a versatile heat source, thereby enabling high precision, stable, and efficient machining.